K-4323 | Genuine Eaton TCM Transmission Control Module EP3

Commonly Used With Eaton AutoShift, Eaton UltraShift, UltraShift PLUS, Fuller Advantage automated transmissions.

These transmissions were installed in many Class 6–8 trucks from manufacturers such as: Peterbilt, Kenworth, Freightliner, International, Volvo Trucks, Mack Trucks, Western Star

1. Controls gear shifting

The TCM decides:

• When to upshift
• When to downshift
• Which gear is best for speed and load

It constantly adjusts based on:

• Vehicle speed
• Engine RPM
• Throttle input
• Driving conditions

2. Improves driving smoothness

The TCM manages shift timing and hydraulic pressure so shifts feel:

• Smooth
• Quick
• Comfortable

It helps prevent:

• Harsh shifts
• Jerking
• Gear hunting

3. Increases fuel economy

By selecting the most efficient gear, the TCM helps:

• Lower engine RPM at cruising speeds
• Reduce fuel consumption
• Improve overall efficiency

4. Protects the transmission

The TCM can detect problems and reduce damage by:

• Entering “limp mode”
• Limiting certain gears
• Adjusting pressure to prevent slipping

This can prevent expensive transmission failure.

5. Adapts to driving style

Many modern TCMs “learn” how you drive:

• Aggressive driving → later shifts, higher RPM
• Gentle driving → earlier shifts for economy

Some vehicles also include:

• Sport mode
• Tow/haul mode
• Manual shift mode

6. Coordinates with the engine computer

The TCM communicates with the engine control system to:

• Reduce engine torque during shifts
• Improve acceleration
• Reduce drivetrain stress

This coordination is important in modern vehicles.

1. Hard or jerky shifting

The transmission may:

• Slam into gear
• Shift very aggressively
• Feel rough between gears

2. Delayed shifting

You press the gas, but the transmission:

• Hesitates before changing gears
• Takes too long to engage Drive or Reverse

3. Transmission stuck in one gear (“limp mode”)

Many vehicles enter a protection mode where:

• The car stays in 2nd or 3rd gear
• Speed and acceleration are limited

This helps prevent transmission damage.

4. Gear slipping

The vehicle may:

• Randomly change gears
• Rev high without accelerating properly
• Feel like it “falls out” of gear

5. Check Engine Light or transmission warning light

A bad TCM often triggers codes such as:

• P0700
• P0600 series
• Shift solenoid codes

A scan tool is usually needed to read them.

6. No shifting at all

The transmission may:

• Refuse to upshift or downshift
• Stay neutral-like
• Fail to engage gears properly

7. Poor fuel economy

Improper shifting can cause:

• Higher RPMs
• Inefficient gear selection
• Increased fuel consumption

8. Erratic or unpredictable shifting

The car may:

• Shift randomly
• Shift at unusual RPMs
• Change behavior from one drive to another

9. Trouble going into Drive or Reverse

You may notice:

• Long delays
• Hard engagement “clunks”
• No response initially